Getting the localized normal of a part

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#1

I am casting a ray onto a block. The returning normal is of course global. By that, i mean it will be a vector that demonstrates the direction the normal facing. How could I get a more localized version? By that, I somehow use the lookvector of the part and the normal of the ray to determine which direction the normal should be facing.

This is the code I am thinking of that could do this, but I am wondering if there are any more optimized ways to do this.

function normal_to_lookvector(cframe: CFrame, normal: Vector3)
	if normal == Vector3.new(0,0,-1) then
		return cframe.LookVector
	elseif normal == Vector3.new(0,0,1) then
		return -cframe.LookVector
	elseif normal == Vector3.new(1,0,0) then
		return cframe.RightVector
	elseif normal == Vector3.new(-1,0,0) then
		return -cframe.RightVector
	--etc
	end
end

I appreciate any help.

#2

Clarification may help, I’m not sure what you’re trying to accomplish.

If you already weren’t aware:
Normals describe a perpendictular vector to a surface, each axis is constrainted between -1 to 1 because it’s a directional vector, not positional.

Example Image

image
image665×755 9.19 KB

What needs to be “localized”?

#3

I’m not really understanding your code snippet because cframe.LookVector is a world-space (global) forward vector of the cframe, while in your written post you are interested in finding the local vector.

You can get the object-space (local) vector of the cframe by using CFrame:VectorToObjectSpace:

cframe:VectorToObjectSpace(normal)

For example, cframe:VectorToObjectSpace(normal.LookVector) should give you approx CFrame.new(0, 0, -1)

If you want to get the world-space vector from the cframe you can use VectorToWorldSpace instead.

#4

I’m sorry, I may have specified what I wanted wrongly. I’m thinking of changing the normal vector depending on the direction a part is facing. I’ll try out your suggestion and tell you how it goes, though I’m going to bed now. Thanks for your reply!

#6

that’s weird, the normal in your diagram (and in a test i just conducted) did have the normal the way i wanted it. for some reason, the normal in my main project was not behaving the same way due to the change in some code. i made this post without knowing that.

however, i do still have that persisting issue in my code.
this is a part of my grid based object placement system.

local object_offset: Vector3 = (ray.Normal * (model_region_space_size[vector_to_axis(ray.Normal)]) / 2)

--model_space_region_space_size is a size vector that shows a region in which the given instance takes up. it takes the very min vertex of the part, and vise versa, and creates a region. this variable is only the size part of that  region
--vector_to_axis turns a vector into a string. e.g Vector3.new(0,1,0) -> "Y"

i’m having an issue where when ray.Instance is rotated by >90 degrees, that axis is off (check vector_to_axis learning comment).

here is an example with my problem more visualized

image
image1253×749 58.6 KB